Espinoza-Corral Roberto, Zavřel Tomáš, Sutter Markus, Leslie Chase H, Yang Kunwei, Beck Warren F, Červený Jan, Kerfeld Cheryl A
MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA.
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
Plant Cell. 2025 Jul 1;37(7). doi: 10.1093/plcell/koaf144.
Phycobilisomes (PBSs) are versatile cyanobacterial antenna complexes that harvest light energy to drive photosynthesis. They can adapt to various light conditions; for example, dismantling under high light to prevent photo-oxidation and arranging in rows under low light to increase light harvesting efficiency. Light quality also influences PBS structure and function, as observed under far-red light exposure. Here, we describe a PBS linker protein, ApcI (previously hypothetical protein Sll1911), expressed specifically under red light (620 nm) or upon chemically induced reduction of the plastoquinone pool. We characterized ApcI in Synechocystis sp. PCC 6803 using mutant analyses, PBS binding experiments, and protein interaction studies. Deletion of apcI conferred high light tolerance on Synechocystis sp. PCC 6803 compared to the wild-type strain, leading to reduced energy transfer from PBSs to the photosystems under high light. Binding experiments revealed that ApcI replaces the linker protein ApcG at the membrane-facing side of the PBS core via a paralogous C-terminal motif. Additionally, the N-terminal region of ApcI interacts with photosystem II. Our findings highlight the importance of PBS remodeling for adaptation to different light conditions. The characterization of ApcI provides insight into the mechanisms by which cyanobacteria optimize light harvesting in response to varying light conditions.
藻胆体（PBSs）是多功能的蓝藻天线复合体，可收集光能以驱动光合作用。它们能够适应各种光照条件；例如，在高光条件下解体以防止光氧化，在低光条件下排列成行以提高光捕获效率。如在远红光照射下所观察到的，光质也会影响藻胆体的结构和功能。在此，我们描述了一种藻胆体连接蛋白ApcI（以前的假定蛋白Sll1911），它在红光（620 nm）下或在化学诱导的质体醌库还原时特异性表达。我们利用突变分析、藻胆体结合实验和蛋白质相互作用研究，对集胞藻PCC 6803中的ApcI进行了表征。与野生型菌株相比，缺失apcI使集胞藻PCC 6803具有高光耐受性，导致在高光条件下从藻胆体到光系统的能量转移减少。结合实验表明，ApcI通过一个同源的C端基序在藻胆体核心面向膜的一侧取代连接蛋白ApcG。此外，ApcI的N端区域与光系统II相互作用。我们的研究结果突出了藻胆体重塑对于适应不同光照条件的重要性。对ApcI的表征为蓝藻响应不同光照条件优化光捕获的机制提供了见解。
